Unit 10 Electrical Measurements

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• Text • Translation of the Text• Notes• Exercises• Oral Practices

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Student: I know there are instruments for measuring different electrical quantities. Could we review them please? ①Engineer: I’d be glad to. A very common device that uses a pointer on a calibrated scale works by using a galvanometer movement.Student: Do all meters using a pointer and a scale work by this mechanism?Engineer: Many of them do. ②Student: How does it work?Engineer: A small coil of wire, free to rotate about a fixed point, is mounted between the poles of permanent magnet. ③The two leads of the moving coil are connected to the respective meter output leads. When current flows through the coil, it becomes an electromagnet that interacts with the permanent magnet.

指针 校准的 刻度盘 电流计

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Student: Is the pointer attached to the coil in some way?Engineer: Yes.Student: Then the coil rotates according to the amount of current flowing through it. Because the pointer is connected to the coil, it moves along the calibrated scale.Engineer: And the current, voltage, power or resistance values are indicated by the pointer’s position or deflection.Student: Voltage, power and resistance? It seems to me that this device can measure only current.Engineer: True. However, we can build many different kinds of circuits aroud the movement to get voltmeters, and ohmmeters, as well as ammeters.

电压表

偏差

安培表欧姆表

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学生：我知道，有一些测量电量的不同的仪器，我们能先回顾一下吗？工程师：我很高兴这样做。有一种非常普通的在校准的刻度盘上使用指针的装置。它是通过使用一个灵敏电流计来工作的。学生：所有的仪表都用指针和度盘以机械方式工作吗？工程师：许多仪表都这样。学生：他们怎样工作呢？工程师：有一个能固定支点转动的线圈安装在永久磁铁的两个极之间，运动线圈的两根引线连接在各自的仪表输出端，当电流通过线圈时，它就变成与永久磁铁相互作用的电磁铁

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学生：指针是以某种方式附在线圈上吗？工程师：是的。学生：那么线圈就按所通过的电流的大小转动。由于指针连在线圈上，它就沿着刻度盘运动。工程师：而且，电流、电压、功率、电阻值就由指针的位置或偏转来指示。学生：电压、功率和电阻？我以为这样的装置只能测量电流。工程师：对。然而，我们可以围绕运动方式生产出不同电路的电压表、瓦特表、欧姆表和电流（安培）表。

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1. Could we review them please?

我们能先回顾一下吗？

Notes

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许多仪表都这样 ( 工作 ) 的。

2. Many of them do.

3. A small coil of wire, free to rotate about a fixed point, is mounted between the poles of

permanent magnet.

有一个能固定支点转动的线圈安装在永久磁铁的两个极之间

Notes

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Exercises

Filling the blanks with the proper terms from the list.

ammeter root-mean-square

ohmmeter scale

oscilloscope voltmeter

pointer wattmeter home

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2. Filling the blanks with the proper terms from the list.

Exercises

(1) A _________ measures electrical power.

(2) The definition of the _________ indicates how much current is flowing through the moving coil.

(3) A calibrated __________ is used for the actual measurements on moving coil meters.

wattmeter

pointer

scale

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2. Filling the blanks with the proper terms from the list.

Exercises

(4) Vultage is measured with a __________.

(5) An ____________ displays a visual picture of variations in a measured voltage.

(6) Resistance is measured with an ___________.

oscilloscope

ohmmeter

voltmater

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2. Filling the blanks with the proper terms from the list.

Exercises

(7) Current is measured with an __________.

(8) All AC values require ____________ meters for measurements.

Root-mean-square

ammeter

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